This invention relates to improved methods and apparatus for controlling input power requirements for delivering radio frequency (RF) power for process operations. RF power is extensively used in a wide variety of applications for carrying out process operations. Exemplary of such process operations is RF induction heating. RF induction heating involves coupling RF power to a material that absorbs the RF power and converts the RF power into heat. In other words, the currents induced in material by the RF power are converted into heat because of the electrical resistance of the material that absorbs the RF power. In this manner, the RF power can be used to heat an object without having physical contact between the power source and the object. This type of heating can be used wherein the object is the material that absorbs the RF power and is heated directly by the RF power. Alternatively, the object may be in contact with or near a second material that absorbs RF power; the second material absorbs the RF power and creates the heat; the heat is then transferred to the workpiece by conduction, convection, or radiation.
In another example of RF heating, the RF power can be coupled to a gas to produce a thermal plasma. Free electrons in the thermal plasma absorb the RF power and are raised to high energy levels. These energetic free electrons interact with other gas phase species to produce a high temperature mixture that can transfer their thermal energy to other gases, liquids, or solids.
The thermal plasmas mentioned above can be used to promote chemical reactions. Chemical reactions can be promoted because of the high temperatures of the thermal plasma. Alternatively, thermal plasmas are able to promote chemical reactions because of the ability of the energetic electrons to break chemical bonds and allow chemical reactions to occur that would proceed with difficulty under non-plasma conditions.
The manufacture of optical fiber preforms is an example of the use of thermal plasmas generated using RF power. The RF thermal plasma provides the energy for driving the chemical reactions in gas mixtures of silicon compounds, oxygen, and dopants. The chemical reactions cause deposition of doped silica layers.
Another example involving RF power thermal plasmas is the operation of high-pressure gas lasers. In gas laser operation the important characteristic of the RF plasma is the light emission that occurs because of the plasma. The thermal energy that is produced is generally not considered important to the operation of the laser.
In other applications, RF power is used to produce non-thermal plasmas, also referred to as non-equilibrium plasmas. The manufacture of semiconductor devices is one area in which non-thermal plasmas are extensively used. The non-thermal plasmas are used for etch processes wherein the non-thermal plasmas are used to generate reactive species in a gas to accelerate reactions between the species and a solid surface. The etch process can be a general removal of components on the surface as in a cleaning process or the selective removal of material from certain areas on the surface through use of a masking material that has been previously patterned. Non-thermal plasmas are used to promote deposition reactions wherein gas phase species are caused to react to form a solid product that deposits on surfaces. During the manufacture of semiconductor devices, etch processes involving RF plasmas and deposition processes involving RF plasmas are used repeatedly during the fabrication process. One of the main benefits of using the non-thermal plasma is the ability of the non-thermal plasma to stimulate chemical reactions that would otherwise require temperatures that are too high for use in the fabrication of semiconductor devices.
RF power non-thermal plasmas are also used as cleaning processes in manufacture of semiconductor devices. The non-thermal plasmas are commonly used to strip photoresist materials from semiconductor wafers as part of post etch wafer clean procedures. The photoresist material serves as a mask material during etch processes used in patterning the surface of the devices. Resist material is stripped from the surface of the wafers by creating a non-thermal plasma in a gas containing oxidizing species such as oxygen and possibly halogen species that are capable of reacting with and volatilizing the resist material. In some applications, the non-thermal plasma is maintained at a position upstream of the wafer. Reactive species generated in the non-thermal plasma flow downstream and react with the wafer surface for the stripping process.
Another cleaning process that uses non-thermal plasmas is the cleaning of reaction chambers used in manufacturing semiconductor devices. Sometimes, the reaction chambers used in plasma etch processes experience a buildup of deposits from the etch process. These deposits must be removed as part of the reactor maintenance process. Also, the reactors that are used in deposition processes for semiconductor device fabrication undergo a buildup of deposits on the reactor walls; the wall deposit must be removed as part of reactor maintenance. Non-thermal plasmas generated using RF power and gases containing species that are reactive with the deposits have been used to volatilize and remove the deposits built up on the walls of etch reactors and deposition reactors.
RF power plasmas have also been used for decomposition of chemical compounds that are hazardous or otherwise undesirable. Some of the compounds are highly refractory in nature and are difficult to decompose. Examples of compounds that have been decomposed or abated with plasmas include chlorofluorocarbons (CFC) and perfluorocompounds (PFC).
The applications given above where RF power is used as part of a process makeup only a small fraction of the applications for RF power. There are numerous additional processing applications for RF power. However, the methods and apparatus typically used to deliver RF power have deficiencies and may be inefficient for use in existing applications. Some of the deficiencies are common for multiple applications. The existing deficiencies in the prior methods and apparatus for RF power delivery may limit the use of RF power for possible new applications.
One frequently encountered problem with standard RF power delivery systems is that the equipment is typically designed for use at only one set of optimized input power conditions. Specifically, the required input current and input voltage only have a small range of values for operation of the RF power delivery system. The narrow operating conditions for input power in terms of current and voltage presents a problem for the typical AC power source lines available in homes, offices, and factories around the world. To accommodate the input power requirements for standard RF power delivery systems, three phase AC power sources are typically required to assure having adequate current and voltage for the power input to the RF power delivery system. Providing three phase AC power sources may require additional wiring if the three phase AC lines are not already available. Consequently, the use of some RF power delivery systems can be hindered by the unavailability of three phase AC electric power. Furthermore, the variation in the standard current and voltage for AC power lines used in different countries can also hinder the use of RF power delivery systems. To overcome these problems, the old-style RF power delivery systems have been required to have special power converters to accommodate the current and voltage sources available in each country.
Based on the variety of possible applications for RF power delivery as described above, there are numerous situations in which it would be advantageous to have an RF power delivery system capable of operating over a wide range of input current and voltage. There is a need for improved RF power delivery methods and apparatus that require a minimum or no special wiring to access the electric power source. In addition, there is a need for RF power delivery systems that can be plugged into any standard AC power lines that are used in offices and factories all over the world. There is a need for RF power delivery methods and apparatus that are simple in operation and have the versatility to handle a wide range of input electric power currents and voltages.
This invention is related to methods and apparatus that can overcome deficiencies of known RF power delivery systems. Practicing this invention makes it possible to achieve RF power delivery to a load for which the required input currents and voltages are controlled to stay with in the capabilities of currents and voltages for the available electric power source.
The electric power characteristics are also referred to as power form. Specifically, the electric power characteristics are the combination of current and voltage that makeup the electric power. A given quantity of electric power can be provided as various combinations of current and voltage. For example, 1000 watts of electric power can have an approximate power form of 10 amps at 100 volts, 20 amps at 50 volts, or 5 amps at 200 volts.
Variable frequency RF power amplifiers are capable of providing an output RF power for which the frequency of the RF power can have values within the frequency range of the RF power amplifier. Usually, the frequencies or rather the ranges of frequencies are varied as part of delivering the RF power to a load for a process operation. For a specified magnitude of RF power and a specified frequency of the RF power, the RF power amplifier requires an input of electric power having a particular current and voltage combination i.e. power form. In other words, the RF power amplifier has specific requirements of input current and voltage in order to provide the specified frequency of the RF power. Consequently, it is possible to adjust the frequency of the RF power and maintain the desired magnitude of the RF power so that the required power form of the input power is varied. This particular behavior of the RF power amplifier can be used with a controller responsive to the input power requirements to automatically adjust the frequency of the output RF power so as to maintain the required power form of the input electric power within the capabilities of the input electric power source.
The frequency is controlled automatically in order to achieve an input requirement of current and voltage that meets the capabilities of the available power source. Further adjustments are made in order to achieve desired, preferably efficient, RF power delivery to the load. The further adjustments may include changes in the impedance that the RF power amplifier sees in delivering RF power to the load or changes in the frequency of the RF power to obtain a frequency that is resonant with coupling RF power to the load.
Aspects of the present invention are accomplished using a power form controller and a variable frequency RF power delivery system. The power form controller is responsive to power characteristics of input power to the RF power delivery system. The controller provides signals to the RF power delivery system to adjust the frequency of the output power from the RF power delivery system so that the required power form for the input power to the RF power delivery system does not exceed the capabilities of the input electric power source.
In different embodiments of the present invention, the variable frequency RF power delivery systems may be of different designs and may use different methods of operation. Examples of variable frequency RF power delivery systems are described in 1999 U.S. Pat. No. 5,892,198 to Barnes et al., 1997 U.S. Pat. No. 5,654,679 to Mavretic et al., 1995 U.S. Pat. No. 5,383,019 to Farrell et al., and 1993 U.S. Pat. No. 5,223,457 to Mintz et al.; all of these applications are incorporated herein by this reference.
Standard variable frequency RF power delivery systems typically include a variable frequency RF power amplifier, a match network, an RF power coupling element, one or more sensors, and one or more controllers. The sensor can include one or more pickups for deriving information about the RF power. The RF power amplifier provides an output RF power through the match network to the RF power coupling element. The sensor collects information about the RF power and provides the information to the controller. The controller responds to information input from the sensor to provide control signals to the RF amplifier to specify the magnitude and frequency of the RF power output. The controller or another controller may provide signals to control impedance matching if the match is a variable match network.
Standard variable frequency RF power delivery systems can be included in embodiments of the present invention. A requirement for using standard variable frequency RF power delivery systems in embodiments of the present invention is that the RF power delivery systems must be capable of being modified to implement power form control. The power form control capability adjusts the base frequency of operation or rather the frequency range of operation in response to characteristics of input electric power for RF power amplifiers in the RF power delivery systems.
Alternatively, variable frequency RF power delivery systems that are more advanced than those commonly known may also be used in embodiments of the present invention. For example, 1999 United States patent application titled xe2x80x9cMethods and Apparatus for RF Power Deliveryxe2x80x9d by Russell F. Jewett and Curtis C. Camus filed on Dec. 31, 1999, incorporated herein by reference, describes an advanced variable frequency RF power delivery system suitable for use in embodiments of the present invention.
An aspect of the present invention is a method of operating a variable frequency RF power delivery system for delivering RF power to a load for a process operation. The method is carried out using a variable frequency RF power source. The variable frequency RF power source includes an RF power amplifier, one or more sensors, and an RF power coupling element disposed so as to couple RF power to the load. The method includes adjusting at least one of:
a) frequency of the delivered RF power; and
b) impedance seen by the RF power source; in response to measurements of RF power delivery efficiency so as to achieve desired, preferably efficient, delivery of the RF power to the load and also automatically adjusting the frequency of the delivered RF power in response to a parameter representative of the current and voltage of the electric power input to the RF power amplifier so as to maintain the input current and voltage within the limits of the available power source.
One embodiment of the present invention is a method of operating a variable frequency RF power delivery system for delivering RF power to a load for a process operation. The method is carried out using a variable frequency RF power source. The variable frequency RF power source includes an RF power amplifier, one or more sensors, and an RF power coupling element disposed so as to couple RF power to the load. The method includes adjusting the frequency of the delivered RF power in response to a parameter representative of the RF power delivery efficiency so as to achieve efficient delivery of the RF power to the load. The method further includes adjusting the frequency of the delivered RF power automatically in response to a parameter representative of the current and voltage of the electric power input to the RF power amplifier so as to maintain the input current and voltage within the limits of the available electric power source.
Another aspect of the present invention is an apparatus for RF power delivery including a variable frequency RF power source and a control system. The control system is capable of adjusting at least one of:
a) frequency of the delivered RF power; and
b) impedance seen by the RF power source; in response to the RF power delivery efficiency so as to achieve desired, preferably efficient, delivery of the RF power to the load. The control system is also capable of adjusting the frequency of the delivered RF power in response to a parameter representative of the current and voltage of the electric power input to the RF power amplifier so as to maintain the input current and voltage within the limits of the available electric power source.
Another aspect of the present invention is an apparatus for RF power delivery including a variable frequency RF power source and a control system. The control system is capable of adjusting the frequency of the delivered RF power in response to a parameter representative of the RF power delivery efficiency so as to achieve desired, preferably efficient, delivery of the RF power to the load and also adjusting the frequency of the delivered RF power in response to a parameter representative of the input power current and voltage of the electric power input to the RF power amplifier so as to maintain the input current and voltage within the limits of the available electric power source.
Suitable control systems for practicing embodiments of the present invention can include one or more controllers for each of the parameters being controlled. Alternatively, suitable control systems may include a single controller that is capable of controlling multiple parameters simultaneously.
In one embodiment, a control system, capable of controlling two or more parameters simultaneously, is used to achieve desired, preferably efficient, RF power delivery to a load. In addition, the control system is used to automatically control the frequency of the delivered RF power in order to achieve efficient use of the available input electric power characteristics.
In another embodiment, the control system is capable of controlling two or more parameters simultaneously. The control system is used to control the frequency in order to achieve desired, preferably efficient, RF power delivery to the load. In addition, the control system is used to control the frequency in order to achieve efficient use of the available input electric power characteristics.
The power form of the input electric power is directly represented by measurements of the current and voltage of the input power. Similarly, the power form of the electric power source is directly represented by the current and voltage available from the electric power source. One embodiment of the present invention includes measuring the current and voltage to obtain the power form of the input electric power. Alternative embodiments of the present invention can use alternative indicators of the input power form. Examples of parameters that are representative of the input power form include input electric power current, input electric power voltage, RF power current, and RF power voltage. Examples of suitable embodiments for controlling the power form of the input electric power through adjustments in the RF power frequency include:
a) minimizing RF voltage by adjusting the RF frequency;
b) minimizing input electric power voltage by adjusting the RF frequency;
c) maximizing input electric power current by adjusting the RF frequency; and
d) maximizing RF current by adjusting the RF frequency. In preferred embodiments the RF voltage and RF current are measured at the RF power coupling element.
Numerous control techniques can be used for adjusting the frequency to control the input power form in embodiments of the present invention. Examples of control techniques that can be used include incrementing and decrementing in fixed amounts, proportional, integral, and derivative techniques and combinations thereof.
According to various aspects of the present invention, embodiments of the RF power coupling element can have any form suitable for RF power delivery. Exemplary forms of RF power coupling elements are antennas, coils, cylindrical coils, planar coils, electrodes, rings, parallel plates, screens, and waveguides. Various types of RF power coupling elements are well known in the art.
In various separate embodiments of the present invention, the load that receives the RF power may use the RF power for different applications. Exemplary functions of the loads for various applications are as follows. The load may absorb the RF power to produce heat for a heating process as in RF induction heating. The load may absorb the RF power to produce a thermal plasma such as those used for chemical processing, materials processing, analytical chemistry, or driving optical devices. The load may absorb the RF power to produce a non-thermal plasma such as those used for chemical processing or materials processing. The load may absorb RF power to produce non-thermal plasmas such as plasmas used for semiconductor device fabrication processes like etching, deposition, cleaning, doping, oxidation, drying, photoresist stripping, parts cleaning, reaction chamber cleaning, and annealing. The load may absorb RF power to produce a plasma for stimulating chemical reactions that cannot proceed or proceed slowly under non-plasma conditions. The load may absorb RF power to produce a plasma for decomposing chemical compounds. The load may absorb RF power to produce a plasma for synthesizing chemical compounds.
In another aspect of the present invention, the delivered RF power is used for abatement of gaseous halogenated organic compounds, other refractory organic compounds, perfluorocompounds, and refractory inorganic compounds. The apparatus uses a non-thermal plasma, generated by RF power, for generating free radicals in a dielectric reaction vessel. In a further aspect of the present invention, the treatment of gases is enhanced by the addition of suitable ancillary reaction gases including water, methane, hydrogen, ammonia, hydrogen peroxide, oxygen, or mixtures thereof.
Embodiments of the present invention provide methods and apparatus for RF power delivery that automatically optimize the frequency of the delivered RF power so as to enable use of a wide variety of available power characteristics for the input power.
Embodiments of the present invention provide methods and apparatus for RF power delivery such that the apparatus has a greater probability of being able to operate with a single phase AC power source in substantially any country in the world.
Embodiments of the present invention provide methods and apparatus for RF power delivery such that the apparatus automatic attempts to optimize use of the available input power source.
Embodiments of the present invention provide methods and apparatus for RF power delivery for heating as in RF induction heating.
Embodiments of the present invention provide methods and apparatus for RF power delivery for generating plasmas.
Embodiments of the present invention provide methods and apparatus for RF power delivery for generating thermal plasmas.
Embodiments of the present invention provide methods and apparatus for RF power delivery for generating non-thermal plasmas.
Embodiments of the present invention provide methods and apparatus for RF power delivery for promoting chemical reactions.
Embodiments of the present invention provide methods and apparatus for RF power delivery for generating plasmas for semiconductor device fabrication steps such as etching, deposition, cleaning, doping, oxidation, drying, photoresist stripping, parts cleaning, reaction chamber cleaning, and annealing.
Embodiments of the present invention provide methods and apparatus for removal of refractory compounds from waste streams. Refractory compounds include compounds that show a high degree of stability with respect to temperature and reactivity and are difficult to decompose.
Embodiments of the present invention provide new and useful methods and apparatus for the destruction of refractory compounds such as perfluorocompounds, such as carbon fluorides, carbon tetrafluoride, nitrogen triflouride, and sulfur hexafluoride by reactions facilitated by a plasma.
Embodiments of the present invention provide methods and apparatus for gas waste treatment using a non-thermal plasma generated by RF power.
Embodiments of the present invention provide methods and apparatus that are suitable for processing waste streams emanating from an individual semiconductor process tool and that can become an integral part of the semiconductor device fabrication process.
An advantage of embodiments of the present invention is the ability to provide an economical apparatus and method for the destruction of refractory compounds contained in gaseous waste streams.
Another advantage of embodiments of the present invention is the ability to provide waste treatment of undiluted off gases from individual semiconductor device fabrication tools. Embodiments of the present invention can be made compact enough to be integrated into and attached directly to one or more than one wafer processing tools.